In the United States and in a number of other countries, a regulatory body like the FCC (Federal Communications Commission), oftentimes regulates the use of radio spectrum in order to fulfill the communications needs of entities such as businesses and local and state governments as well as individuals. More specifically, the FCC licenses a number of spectrum segments to entities and individuals for commercial or public use. These licenses may allow these entities and individuals (“licensees”) an exclusive right to utilize their respective licensed spectrum segments for a particular geographical area for a certain amount of time. Such licensed spectrum segments are believed to be necessary in order to prevent or mitigate interference from other sources. However, if particular spectrum segments are not in use at a particular location at a particular time (“the available spectrum”), another device should be able to utilize such available spectrum for communications. Such utilization of the available spectrum would make for a much more efficient use of the radio spectrum or portions thereof.
Cognitive Radios (CRs) are seen as a solution to the current low usage or under utilization of the radio spectrum. It is a technology that will enable flexible, efficient and reliable spectrum use by adapting the radio's operating characteristics to the real-time conditions of the environment. CRs have the potential to utilize the large amount of unused spectrum in an intelligent way while not interfering with other incumbent devices in frequency bands already licensed for specific uses. CRs are enabled by the rapid and significant advancements in radio technologies (e.g., software-defined radios, frequency agility, power control, etc.), and can be characterized by the utilization of disruptive techniques such as wide-band spectrum sensing, real-time spectrum allocation and acquisition, and real-time measurement dissemination.
Accordingly, there is a need in the industry for spectrum sensing algorithms and methods in the CR system to locate unoccupied spectrum segments in an efficient and accurate manner. Constraints of such spectrum sensing algorithms and methods may include the primary spectrum users not providing any spectrum usage information for the CR users.
Additional constraints may include the primary spectrum user signals coming from transmitters located at the proximities of CR receivers or at very distant places. Thus, spectrum-sensing algorithms and methods may need to detect the primary signals with extremely low power-level even below the sensitivity requirement of the link between the incumbent spectrum users. Moreover, these primary spectrum user signals or CR user signal may have the signal power enough to go beyond the CR receiver's dynamic range. This wide dynamic range of received signals may be a very challenging issue to guarantee the detection sensitivity as well as the detection reliability. When a threshold value is applied to this wide range of signal level case, it may cause mis-detection events for the sake of false alarm rate. Otherwise, it may increase false alarm rate to provide better detection sensitivity. Therefore, the threshold selection may be an important factor for the uniform performance of the spectrum sensing algorithms and methods.
Once the above described constraints are addressed, a further constraint is that the time consumed to detect or sense the spectrum over wideband frequency span should be minimized. In other words, the sensing time should be minimized to improve the overall spectral efficiency through the spectrum sensing algorithms and methods. Accordingly, there is a need in the industry for spectrum sensing algorithms and methods in the CR system to locate unoccupied spectrum segments in an efficient and accurate manner.